The invention relates to an improved process for converting hydrocarbons, preferably non-aromatic hydrocarbons, in the presence of an improved zeolite material, to aromatic hydrocarbons and lower olefin hydrocarbons preferably with a low rate of coke formation during the conversion of such hydrocarbons in the presence of such improved zeolite material.
It is known to catalytically crack gasoline boiling range hydrocarbons (in particular, non-aromatic gasoline boiling range hydrocarbons, more in particular, paraffins and olefins) to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene, and xylene, and also ethylbenzene) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N.Y. Chen et al. in Industrial and Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction product of this catalytic cracking process contains a multitude of hydrocarbons such as unconverted C5+ alkanes, lower alkanes (methane, ethane, propane), lower alkenes (ethylene and propylene), C6-C8 aromatic hydrocarbons (e.g., benzene, toluene, xylene, and ethylbenzene), and C9+ aromatic hydrocarbons. Depending upon the relative market prices of the individual reaction products, it can be desirable to increase the yield of certain of the more valuable products relative to the others.
One concern with the use of zeolite catalysts in the conversion of hydrocarbons to aromatic hydrocarbons and lower olefins is the excessive production of coke during the conversion reaction. The term xe2x80x9ccokexe2x80x9d refers to a semi-pure carbon generally deposited on the metal surfaces of process equipment or a catalyst. Coke formed during the zeolite catalyzed aromatization of hydrocarbons tends to cause catalyst deactivation. It is desirable to improve processes for the aromatization of hydrocarbons, and the formation of lower olefins from hydrocarbons, by minimizing the amount of coke formed during such processes. It is also desirable to have a zeolite catalyst that is useful in producing significant quantities of the aromatic and olefin conversion products.
It is an object of this invention to provide a zeolite catalyst composition used to at least partially convert hydrocarbons to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene, xylene and ethylbenzene, i.e., BTX).
A further object of this invention is to provide an improved process for the conversion of hydrocarbons in which the rate of coke formation during such conversion of hydrocarbons is minimized.
A yet further object of this invention is to provide an improved zeolite material which, when used in the conversion of hydrocarbons, results in less coke formation than alternative zeolite materials.
Another object of this invention is to provide an improved zeolite material that gives an improved yield of lower olefins when such improved zeolite material is utilized in the conversion of hydrocarbons.
Yet another object of this invention is to provide hydrocarbon conversion processes which have an acceptably low coke production rate and/or which produce a conversion product containing suitable quantities of lower olefins and BTX aromatics.
Yet another further object of this invention is to provide a method for making an improved zeolite material having such desirable properties as providing for low coke production and improved yields of lower olefins, with an especially improved ratio of lower olefins to aromatics in the product, when used in the conversion of hydrocarbons.
One embodiment of the invention is a novel process of making a zeolite catalyst composition used in the conversion of hydrocarbons, preferably non-aromatic hydrocarbons, to aromatic hydrocarbons and lower olefins. The novel process comprises ion-exchanging the original ions (specifically cations) such as, for example, alkali metal ions or alkaline earth metal ions, of a zeolite with hydrogen ions by acid-treating such zeolite. The cations, preferably hydrogen ions, of such acid-treated zeolite are then further ion-exchanged with ions of zinc and at least one other metal selected from the group of metals consisting of Group 6B of the periodic table of elements to thereby provide an acid-treated, ion-exchanged zeolite. The ion-exchange of such acid-treated zeolite occurs in the presence of an ion-exchange medium, preferably comprising an aqueous solution of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal, which promotes the exchange of ions of the acid-treated zeolite with ions of zinc and at least one other metal. The acid-treated, ion-exchanged zeolite is then subjected to a steam treatment to provide the final improved zeolite catalyst composition.
Another embodiment of the invention is a process for the conversion of non-aromatic hydrocarbons to aromatic hydrocarbons and lower olefins by contacting, under conversion conditions, a hydrocarbon-containing fluid with an acid-treated, ion-exchanged, steam-treated zeolite catalyst composition.
Yet another embodiment of the invention is the novel composition of an acid-treated zeolite of which the ions of such zeolite have been ion-exchanged with ions of zinc and at least one other metal selected from the group of metals consisting of Group 6B of the periodic table of elements. The acid-treated, ion-exchanged zeolite is then subjected to a steam treatment to provide the final improved zeolite catalyst composition.
Yet another embodiment of the invention is the novel composition, i.e., product, made by the novel process of ion-exchanging the original ions (specifically cations) such as, for example, alkali metal ions or alkaline earth metal ions, of a zeolite with ions of hydrogen by acid-treating such zeolite. The cations, preferably hydrogen ions, of such acid-treated zeolite are then farther ion-exchanged with ions of zinc and at least one other metal from the group of metals consisting of Group 6B of the periodic table of elements. The ion-exchange of such acid-treated zeolite occurs in the presence of an ion-exchange medium, preferably comprising an aqueous solution of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal, which promotes the exchange of ions of the acid-treated zeolite with ions of zinc and at least one other metal. The acid-treated, ion-exchanged zeolite is then subjected to a steam treatment to provide the final improved zeolite catalyst composition.
Other objects and advantages of the invention will become apparent from the detailed description and the appended claims.
The inventive composition includes a zeolite starting material that has been ion-exchanged such that a predominant proportion of such zeolite""s exchangeable ions (specifically cations) are hydrogen (H+) ions. Preferably, such zeolite starting material has been treated with an acid to thereby provide an acid-treated zeolite in which a predominant proportion of such acid-treated zeolite""s exchangeable ions (specifically cations) are hydrogen (H+) ions. In general, it is contemplated that more than 50 percent and preferably more than 75 percent of the cationic sites of such acid-treated zeolite will be occupied by hydrogen ions. After further ion-exchange of such acid-treated zeolite, the resulting inventive composition further contains ions of zinc and at least one other metal or element selected from the group of elements consisting of Group 6B of the periodic table of elements. It is understood herein that any reference to at least one other metal in addition to zinc contained in the inventive composition will be an element from the Group 6B elements including Chromium (Cr), Molybdenum (Mo), and Tungsten (W). As the term is used within this description and in the claims, any reference to metals will include zinc and those Group 6B elements listed above.
An important aspect of the invention is the requirement that the original ions (specifically cations), such as, for example, alkali metal ions or alkaline earth metal ions, of a zeolite preferably be ion-exchanged with hydrogen ions (H+) by acid-treating such zeolite to provide an acid-treated zeolite. While less preferred, the original ions of the zeolite may be ion-exchanged with hydrogen ions (H+) via initial ammonium exchange followed by calcination.
The cations, preferably hydrogen ions, of such acid-treated zeolite are then dual ion-exchanged, i.e., simultaneously ion-exchanged with ions of zinc and at least one other metal in the presence of an ion-exchange medium, preferably comprising an aqueous solution of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal, which promotes the exchange of ions of the acid-treated zeolite with ions of zinc and at least one other metal. The dual or simultaneous ion-exchange of such acid-treated zeolite in the presence of such ion-exchange medium creates an equilibrium (i.e., competitional) ion-exchange environment in which the ammonium ions (NH4+) of the ammonium-containing compound attempt to exchange with the cations, preferably hydrogen ions, of the acid-treated zeolite. However, the ammonium ions must xe2x80x9ccompetexe2x80x9d with the ions of zinc and at least one other metal to ion-exchange (hence the term xe2x80x9ccompetitional ion-exchangexe2x80x9d) with the cations of the acid-treated zeolite. The competitional ion-exchange environment allows for a better dispersion of the ions of zinc and at least one other metal within the acid-treated zeolite.
A yet farther important aspect of the novel process of making the catalyst is a steam-treating step. The steam-treating step includes a steam treatment of the acid-treated, ion-exchanged zeolite subsequent to such ion-exchange, as described above, of the original ions of a zeolite with ions of zinc and at least one other metal. The use of the steam-treatment step produces an acid-treated, ion-exchanged, steam-treated zeolite catalyst composition containing ions of zinc and at least one other metal that provides an improved lower olefin yield and an improved (i.e., greater) olefins-to-aromatics ratio when used in the conversion of hydrocarbons, preferably non-aromatic hydrocarbons, than a catalyst made by certain methods other than the inventive method described herein.
To make the improved zeolite catalyst having been ion-exchanged with ions of zinc and at least one other metal, a starting zeolite or zeolite material is, preferably, first treated with an acid to form an acid-treated zeolite in which the original ions (specifically cations) such as, for example, alkali metal ions or alkaline earth metal ions, of the starting zeolite or zeolite material are ion-exchanged with hydrogen ions (H+). Methods known to one skilled in the art can be used to ion-exchange the zeolite starting material with hydrogen ions such as those disclosed in U.S. Pat. No. 5,516,956, the disclosure of which is incorporated herein by reference.
The zeolite starting material used in the composition of the invention can be any zeolite which is effective in the conversion of hydrocarbons, preferably non-aromatic hydrocarbons, to lower olefin hydrocarbons and aromatic hydrocarbons when contacted under suitable reaction conditions. Examples of suitable zeolites include, but are not limited to, those disclosed in Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 15, pages 638-669 (John Wiley and Sons, New York, 1981). Preferably, the zeolite has a constraint index (as defined in U.S. Pat. No. 4,097,367, which is incorporated herein by reference) in the range of from about 0.4 to about 12, preferably in the range of from about 2 to about 9. Generally, the molar ratio of SiO2 to Al2O3 in the crystalline framework of the zeolite is at least about 5:1 and can range up to infinity. Preferably the molar ratio of SiO2 to Al2O3 in the zeolite framework is in the range of from about 8:1 to about 200:1, more preferably in the range of from about 12:1 to about 100:1. Preferred zeolites include ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-38, and combinations thereof. Some of these zeolites are also known as xe2x80x9cMFIxe2x80x9d or xe2x80x9cPentasilxe2x80x9d zeolites. The presently more preferred zeolite is ZSM-5.
To produce a zeolite in the hydrogen-exchanged form, the zeolite starting material is, preferably, treated with an acid by any suitable means or method(s) that result in an acid-treated zeolite. Generally, any organic acid, inorganic acid, or combinations thereof can be used in the process of the present invention so long as the acid provides a source of hydrogen ions for exchange with the original ions (specifically cations), such as, for example, alkali metal ions or alkali earth metal ions, of the zeolite. The acid can also be a diluted aqueous acid solution. Examples of possible acids include, but are not limited to, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, trifluoroacetic acid, trichloroacetic acid, p-toluenesulfonic acid, methanesulfonic acid, partially neutralized acids wherein one or more protons have been replaced with, for example, a metal (preferably an alkali metal), and combinations thereof. Examples of partially neutralized acids include, but are not limited to, sodium bisulfate, sodium dihydrogen phosphate, potassium hydrogen tartarate, ammonium sulfate, ammonium chloride, ammonium nitrate, and combinations thereof. The presently preferred acid is aqueous hydrochloric acid.
Any method(s) known to one skilled in the art for treating a solid catalyst with an acid can be used in the acid treatment of the present invention. Generally, a zeolite material can be suspended in an acid solution. The concentration of the zeolite in the acid solution can be in the range of from about 0.01 gram per liter to about 500 grams per liter, preferably in the range of from about 0.1 gram per liter to about 400 grams per liter, more preferably in the range of from about 1 gram per liter to about 350 grams per liter, and most preferably in the range from 5 grams per liter to 300 grams per liter. The amount of acid required is the amount that can maintain the solution in acidic pH (i.e., pH less than about 7) during the treatment. Preferably, the initial pH of the acid solution containing a zeolite is adjusted to lower than about 6, preferably lower than about 5, more preferably lower than about 4, and most preferably lower than 3.
Upon the pH adjustment of the solution, the solution can be subjected to a treatment at a temperature in the range of from about 30xc2x0 C. to about 200xc2x0 C., preferably in the range of from about 50xc2x0 C. to about 150xc2x0 C., and most preferably in the range from 70xc2x0 C. to 120xc2x0 C. for a time period in the range of from about 1 minute to about 30 hours, preferably in the range of from about 5 minutes to about 25 hours, and most preferably in the range from 10 minutes to 20 hours. The treatment can be carried out under a pressure in the range of from about atmospheric to about 150 pounds per square inch absolute (psia), preferably about atmospheric, so long as the desired temperature can be maintained.
Thereafter, the acid-treated zeolite material can be washed with running water for a time period in the range of from about 1 minute to about 60 minutes followed by drying, at a temperature in the range of from about 50xc2x0 C. to about 1000xc2x0 C., preferably in the range of from about 75xc2x0 C. to about 750xc2x0 C., and most preferably in the range from 100xc2x0 C. to 650xc2x0 C. for a time period in the range of from about 0.5 hour to about 15 hours, preferably in the range of from about 1 hour to about 12 hours, and most preferably in the range from 1 hour to 10 hours, to produce an acid-treated zeolite. Any drying method(s) known to one skilled in the art such as, for example, air drying, heat drying, spray drying, fluidized bed drying, or combinations thereof can be used.
The dried, acid-treated zeolite can also be further washed, if desired, with a mild acid solution such as, for example, ammonium nitrate which is capable of maintaining the pH of the wash solution in acidic range (i.e., a pH of less than about 7). The volume of the acid generally can be the same volume as the acid for reducing the alumina content in a zeolite. The mild acid treatment can be carried out under substantially the same conditions as disclosed above for the preparation of an acid-treated zeolite. Thereafter, the resulting solid can be washed and dried as disclosed above.
The dried, acid-treated zeolite, whether it has been further washed with a mild acid or not, can be calcined, if desired, under conditions known to those skilled in the art. Generally, such conditions can include a temperature in the range of from about 250xc2x0 C. to about 1,000xc2x0 C., preferably in the range of from about 350xc2x0 C. to about 750xc2x0 C., and most preferably in the range from 450xc2x0 C. to 650xc2x0 C. and a pressure in the range of from about 7 pounds per square inch absolute (psia) to about 750 psia, preferably in the range of from about 7 psia to about 450 psia, and most preferably in the range from 7 psia to 150 psia for a time period in the range of from about 1 hour to about 30 hours, preferably in the range of from about 2 hours to about 20 hours, and most preferably in the range from 3 hours to 15 hours.
The acid-treated zeolite is then treated in an ion-exchange medium selected from the group consisting of water, organic solvents, and combinations thereof. Ion-exchange medium refers to any medium that permits the ion-exchange of such acid-treated zeolite. Typical organic solvents include alcohols, esters, ethers, ketones, and the like and combinations thereof. The preferred ion-exchange medium is water.
The ion-exchange medium, preferably water, further comprises an ammonium-containing compound, a zinc-containing compound and a compound containing at least one other metal. An ammonium-containing compound refers to a compound containing an exchangeable ammonium ion, for example NH4+. A zinc-containing compound refers to a compound containing an exchangeable zinc ion, for example Zn+2. A compound containing at least one other metal refers to a compound containing an exchangeable ion of at least one other metal, for example Cr+3. Preferably, the acid-treated zeolite is treated in an ion-exchange medium comprising an aqueous solution of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal.
Examples of suitable ammonium-containing compounds include, but are not limited to, ammonium nitrate, ammonium sulfate, ammonium chloride, ammonium bromide, ammonium fluoride, and combinations thereof. The preferred ammonium-containing compound is ammonium nitrate. Treatment of the zeolite in an ion-exchange medium comprising an aqueous solution of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal creates an environment in which the ammonium ions compete, with the ions of zinc and at least one other metal, to exchange with the cations, preferably hydrogen ions, of the acid-treated zeolite.
A novel, yet not fully understood, aspect of this invention is the reaction mechanism(s) in which the cations, preferably hydrogen ions, of the acid-treated zeolite are ion-exchanged with ions of zinc and at least one other metal. Wishing not to bound by any theory, one possible reaction mechanism is that the cations of the acid-treated zeolite may initially ion-exchange with ammonium ions of which such ammonium ions are further ion-exchanged with ions of zinc and at least one other metal. Another possible reaction mechanism is that the cations of the acid-treated zeolite may be simultaneously ion-exchanged with ions of ammonium, zinc, and at least one other metal. Yet another possible reaction mechanism is that the higher ion-binding forces of zinc and at least one other metal hinder the ammonium ions from exchanging with the cations of the acid-treated zeolite, allowing mostly ions of zinc and at least one other metal to exchange with the cations of the acid-treated zeolite. Any of these possible reaction mechanisms may be occurring and may even be occurring simultaneously.
Generally, an acid-treated zeolite can be suspended in a solution, preferably an aqueous solution, of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal. The concentration of the acid-treated zeolite in such aqueous solution can be in the range of from about 0.01 gram of acid-treated zeolite per liter of aqueous solution (gm/L) to about 200 gm/L, preferably in the range of from about 0.1 gm/L to about 150 gm/L, more preferably in the range of from about 1 gm/L to about 100 gm/L, and most preferably in the range from 5 gm/L to 75 gm/L.
The amount of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal in the aqueous solution depends on the amount of the original ion(s) to be exchanged. Generally, the concentration of an ammonium-containing compound in the aqueous solution can be in the range of from about 0.1 gram of ammonium-containing compound per liter of aqueous solution (gm/L) to about 500 gm/L, preferably in the range of from about 10 gm/L to about 400 gm/L, more preferably in the range of from about 20 gm/L to about 300 gm/L, and most preferably in the range from 50 gm/L to 200 gm/L.
Generally, the concentration of a zinc-containing compound in the aqueous solution can be in the range of from about 0.1 gram of zinc-containing compound per liter of aqueous solution (gm/L) to about 500 gm/L, preferably in the range of from about 1 gm/L to about 400 gm/L, more preferably in the range of from about 10 gm/L to about 300 gm/L, and most preferably in the range from 20 gm/L to 200 gm/L.
Generally, the concentration of a compound containing at least one other metal in the aqueous solution can be in the range of from about 0.1 gram of compound containing at least one other metal per liter of aqueous solution (gm/L) to about 500 gm/L, preferably in the range of from about 1 gm/L to about 400 gm/L, more preferably in the range of from about 10 gm/L to about 300 gm/L, and most preferably in the range from 20 gm/L to 200 gm/L.
Upon the preparation of an acid-treated zeolite suspended in a solution, preferably aqueous solution, of an ammonium-containing compound, a zinc-containing compound, and a compound containing at least one other metal, the solution can be subjected to a temperature in the range of from about 30xc2x0 C. to about 200xc2x0 C., preferably in the range of from about 40xc2x0 C. to about 150xc2x0 C., and most preferably in the range from 50xc2x0 C. to 125xc2x0 C. for a time period in the range of from about 1 hour to about 100 hours, preferably in the range of from about 1 hour to about 50 hours, and most preferably in the range from 2 hours to 25 hours, depending on desired degrees of ion exchange, and under a pressure in the range of from about atmospheric to about 150 pounds per square inch absolute (psia), preferably in the range of from about atmospheric to about 80 psia, or any pressure that can maintain the required temperature. Thereafter, the acid-treated, ion-exchanged zeolite can be washed with running water for a time period in the range of from about 1 minute to about 60 minutes followed by drying and calcining to produce an acid-treated, ion-exchanged, calcined zeolite. The drying and calcining processes can be carried out substantially the same as those disclosed above for the preparation of an acid-treated zeolite.
The acid-treated, ion-exchanged zeolite is then subjected to a steam treatment whereby it is exposed by any suitable means or method(s) known in the art to an atmosphere of steam under process conditions that suitably provide an acid-treated, ion-exchanged, steam-treated zeolite. The acid-treated, ion-exchanged zeolite is exposed to a predominantly gaseous atmosphere, preferably an entirely gaseous atmosphere, comprising steam. The steam atmosphere preferably has a concentration of steam exceeding about 90 molar percent and, most preferably, the concentration of the steam atmosphere exceeds about 95 molar percent.
The steam treatment may be conducted at any pressure and temperature conditions that suitably provide the acid-treated, ion-exchanged, steam-treated zeolite. Generally, the steam treatment may be conducted at a pressure in the range of from below atmospheric upwardly to about 1000 pounds per square inch absolute (psia). More typical pressures, however, are in the range of from about atmospheric to about 100 psia. The steam treatment temperature is generally in the range of from about 100xc2x0 C. to about 1000xc2x0 C. Preferably, this temperature is in the range of from about 101xc2x0 C. to about 800xc2x0 C. and, most preferably, the steam treatment temperature is in the range from 102xc2x0 C. to 700xc2x0 C.
The time period for conducting the steam treatment step must be sufficient to provide an acid-treated, ion-exchanged, steam-treated zeolite suitable for providing a zeolite catalyst composition having desired properties such as low coke formation and improved lower olefin yield. Generally, the time period for exposing the acid-treated, ion-exchanged zeolite to the atmosphere of steam at appropriate temperature conditions can be in the range of from about 0.1 hour to about 30 hours. Preferably, the steam treatment step is conducted for a time period in the range of from about 0.25 hour to about 25 hours and, most preferably, in the range from 0.5 hour to 20 hours.
Examples of a potentially suitable zinc-containing compound for use in ion-exchanging the ions of the acid-treated.zeolite with zinc ions include, but are not limited to, zinc nitrate, hydrated zinc nitrate, zinc acetate dehydrate, zinc acetylacetonate hydrate, zinc bromide, zinc carbonate hydroxide, zinc chloride, zinc cyclohexanebutyrate dihydrate, zinc 2-ethylhexanoate, zinc 2-ethylhexanoate, zinc fluoride, zinc fluoride tetrahydrate, zinc hexafluoroacetylacetonate dihydrate, zinc iodide, zinc molybdate, zinc naphthenate, zinc nitrate hexahydrate, zinc perchlorate hexahydrate, zinc phosphate hydrate, zinc phthalocynine, zinc protoporphyrin, zinc selenide, zinc sulfate monohydrate, zinc sulfide, zinc telluride, zinc tetrafluoroborate hydrate, zinc meso-tetraphenylprophine, zinc titanate, zinc trifluoromethanesulfonate, and combinations thereof.
The preferred zinc-containing compound is zinc nitrate, more preferably hydrated zinc nitrate, and most preferably zinc nitrate hexahydrate as these zinc-containing compounds are readily available and effective for ion-exchange of the zinc ions of the zinc-containing compound with the ions of the acid-treated zeolite.
The at least one other metal for use in ion-exchange with the acid-treated zeolite can be any Group 6B metal-containing compound that can promote the ion-exchange of the metal ions of the metal-containing compound with the ions of the acid-treated zeolite.
Examples of suitable chromium-containing compounds include, but are not limited to, chromium(II) acetate, chromium(III) acetate, chromium(III) acetylacetonate, chromium(II) chloride, chromium(III) chloride, chromium(II) fluoride, chromium(III) fluoride, chromium(III) nitrate, hydrated chromium (III) nitrate, chromium (III) nitrate monohydrate chromium nitride, chromium(III) perchlorate, chromium(III) potassium sulfate, chromium(III) sulfate, chromium(III) telluride, and combinations thereof.
Examples of suitable molybdenum-containing compounds include, but are not limited to, molybdenum(II) acetate, ammonium molybdate, ammonium dimolybdate, ammonium heptamolybdate, phosphomolybdic acid, molybdenum(III) bromide, molybdenum(II) chloride, molybdenum(IV) chloride, molybdenum(V) chloride, molybdenum(IV) sulfide, sodium molybdate, potassium molybdate, molybdenum fluoride, and combinations thereof.
Examples of suitable tungsten-containing compounds include, but are not limited to, tungsten(V) bromide, tungsten(IV) chloride, tungsten(VI) chloride, tungsten(IV) sulfide, tungstic acid, and combinations thereof.
The preferred metal-containing compound is chromium (III) nitrate, more preferably hydrated chromium (III) nitrate, and most preferably chromium (III) nitrate nonahydrate as these metal-containing compounds are readily available and effective for ion-exchange of the chromium ions of the metal-containing compound with the ions of the acid-treated zeolite.
The amounts of zinc and at least one other metal ion-exchanged with the acid-treated zeolite should be such as to give concentrations, of such metals in the final improved zeolite catalyst composition, effective in providing the desirable properties of favorable (i.e., greater) olefin conversion yields, favorable (i.e., greater) olefins-to-aromatics ratio, and low coke production when the improved zeolite catalyst composition, as manufactured by the process described herein, is employed in the conversion of hydrocarbons, preferably non-aromatic hydrocarbons.
Generally, the amount of zinc and at least one other metal ion-exchanged with the acid-treated zeolite is such that the atomic ratio of the at least one other metal to zinc in the final improved zeolite catalyst composition is in the range of from about 0.1:1 to about 10:1. A preferred atomic ratio of the at least one other metal to zinc in the final improved zeolite catalyst composition is in the range of from about 0.2:1 to about 6:1 and, most preferably, the atomic ratio of the at least one other metal to zinc is in the range from 0.5:1 to 5:1.
Generally, the amount of zinc ion-exchanged with the acid-treated zeolite is such that the weight percent of zinc present in the final improved zeolite catalyst composition is generally in the range upwardly to about 10 weight percent of the total weight of the final improved zeolite catalyst composition. The preferred concentration of the zinc component in the final improved zeolite catalyst composition is in the range of from about 0.1 weight percent of the total weight of the final improved zeolite catalyst composition to about 10 weight percent of the total weight of the final improved zeolite catalyst composition and, most preferably, in the range from 0.5 weight percent of the total weight of the final improved zeolite catalyst composition to 5 weight percent of the total weight of the final improved zeolite catalyst composition.
Generally, the amount of the at least one other metal ion-exchanged with the acid-treated zeolite is such that the weight percent of the at least one other metal present in the final improved zeolite catalyst composition is generally in the range upwardly to about 10 weight percent of the total weight of the final improved zeolite catalyst composition. The preferred concentration of the at least one other metal in the final improved zeolite catalyst composition is in the range of from about 0.1 weight percent of the total weight of the final improved zeolite catalyst composition to about 10 weight percent of the total weight of the final improved zeolite catalyst composition and, most preferably, in the range from 0.5 weight percent of the total weight of the final improved zeolite catalyst composition to 5 weight percent of the total weight of the final improved zeolite catalyst composition.
The improved zeolite catalyst composition described herein can also contain an inorganic binder (also called matrix material) preferably selected from the group consisting of alumina, silica, alumina-silica, aluminum phosphate, clays (such as bentonite), and combinations thereof. The content of the zeolite component (e.g., acid-treated zeolite, acid-treated, ion-exchanged zeolite, or acid-treated, ion-exchanged, steam-treated zeolite) of the optional mixture, of zeolite component and inorganic binder, is in the range of from about 1 weight percent of the total weight of the optional mixture to about 99 weight percent of the total weight of the optional mixture. Preferably, the content of the zeolite component of the optional mixture is in the range of from about 5 weight percent of the total weight of the optional mixture to about 80 weight percent of the total weight of the optional mixture.
Any suitable means for mixing the zeolite component and binder can be used to achieve the desired dispersion of the materials in the resulting admixture. Many of the possible mixing means suitable for use in preparing the mixture of zeolite component and binder of the inventive method are described in detail in Perry""s Chemical Engineers"" Handbook, Sixth Edition, published by McGraw-Hill, Inc., copyright 1984, at pages 21-3 through 21-10, which pages are incorporated herein by reference. Thus, suitable mixing means can include, but are not limited to, such devices as tumblers, stationary shells or troughs, Muller mixers, which are either batch type or continuous type, impact mixers, and the like.
It can be desirable to form an agglomerate of the mixture of zeolite component and binder. Any suitable means known by those skilled in the art for forming such an agglomerate can be used. Such methods include, for example, molding, tableting, pressing, pelletizing, extruding, tumbling, and densifying. Further discussion of such methods is provided in a section entitled xe2x80x9cSize Enlargementxe2x80x9d in Perry""s Chemical Engineers"" Handbook, Sixth Edition, published by McGraw-Hill, Inc., copyright 1984, at pages 8-60 through 8-72, which pages are incorporated herein by reference.
Generally, the zeolite and inorganic binder components are compounded and subsequently shaped (such as by pelletizing, extruding or tableting) into a compounded composition. Generally, the surface area of the compounded composition is in the range of from about 50 m2/g to about 700 m2/g. Generally, the particle size of the compounded composition is in the range of from about 1 mm to about 10 mm.
Any suitable hydrocarbon-containing fluid which comprises paraffins (alkanes) and/or olefins (alkenes) and/or naphthenes (cycloalkanes), wherein each of these hydrocarbons contains in the range of from about 2 carbon atoms per molecule to about 16 carbon atoms per molecule, can be used as the fluid to be contacted with the improved zeolite catalyst composition under suitable process conditions for obtaining a reaction product comprising lower olefins (alkenes, such as ethylene and propylene) containing in the range of from about 2 carbon atoms per molecule to about 5 carbon atoms per molecule and aromatic hydrocarbons (such as BTX, i.e., benzene, toluene, and xylene). Frequently, the suitable hydrocarbon-containing fluid also contains aromatic hydrocarbons. The term xe2x80x9cfluidxe2x80x9d is used herein to denote gas, liquid, vapor, or combinations thereof.
Non-limiting examples of suitable, available hydrocarbon-containing fluid include gasolines from catalytic oil cracking (e.g., FCC and hydrocracking) processes, pyrolysis gasolines from thermal hydrocarbon- (e.g., ethane, propane, and naphtha) cracking processes, naphthas, gas oils, reformates, straight-run gasoline and combinations thereof. Though the particular composition of the fluid is not critical, the preferred hydrocarbon-containing fluid is a gasoline-boiling range hydrocarbon-containing fluid suitable for use as at least a gasoline blend stock generally having a boiling range of about 30xc2x0 C. to about 210xc2x0 C. Generally, the content of paraffins exceeds the combined content of olefins, naphthenes and aromatics (if present).
The hydrocarbon-containing fluid can be contacted by any suitable means, method(s), or manner with the improved zeolite catalyst composition, described herein, contained within a reaction zone. i.e., conversion zone. The contacting step can be operated as a batch process step or, preferably, as a continuous process step. In the latter operation, a solid catalyst bed, or a moving catalyst bed, or a fluidized catalyst bed can be employed. Any of these operational modes have advantages and disadvantages, and those skilled in the art can select the one most suitable for a particular fluid and catalyst.
The contacting step is preferably carried out within a conversion zone, wherein is contained the improved zeolite catalyst composition, and under reaction conditions, i.e., conversion conditions, that suitably promote the formation of olefins, preferably lower olefins (i.e., light olefins such as ethylene and propylene), and aromatics, preferably BTX, from at least a portion of the hydrocarbons of the hydrocarbon-containing fluid. Thus, the reaction product, i.e., the conversion product, includes olefins and aromatics.
Reaction, or conversion, conditions would include a reaction temperature of the contacting step preferably in the range of from about 400xc2x0 C. to about 800xc2x0 C., more preferably in the range of from about 450xc2x0 C. to about 750xc2x0 C. and, most preferably in the range from 500xc2x0 C. to 700xc2x0 C. The contacting pressure can be in the range of from below atmospheric pressure upwardly to about 500 pounds per square inch absolute (psia), preferably, from about atmospheric to about 450 psia and, most preferably, from 20 psia to 400 psia.
The flow rate at which the hydrocarbon-containing fluid is charged (i.e., the charge rate of hydrocarbon-containing fluid) to the conversion zone is such as to provide a weight hourly space velocity (xe2x80x9cWHSVxe2x80x9d) in the range of from exceeding 0 hourxe2x88x921 upwardly to about 1000 hourxe2x88x921. The term xe2x80x9cweight hourly space velocityxe2x80x9d, as used herein, shall mean the numerical ratio of the rate at which a hydrocarbon-containing fluid is charged to the conversion zone in pounds per hour divided by the pounds of catalyst contained in the conversion zone to which the hydrocarbon-containing fluid is charged. The preferred WHSV of the hydrocarbon-containing fluid to the conversion zone can be in the range of from about 0.25 hourxe2x88x921 to about 250 hourxe2x88x921 and, most preferably in the range from 0.5 hourxe2x88x921 to 100 hourxe2x88x921 .
The process effluent from the conversion zone generally contains: a light gas fraction comprising hydrogen and methane, a C2-C3 fraction containing ethylene, propylene, ethane, and propane, an intermediate fraction including non-aromatic compounds having greater than 3 carbon atoms, a BTX aromatic hydrocarbons fraction (benzene, toluene, ortho-xylene, meta-xylene and para-xylene), and a C9+ fraction which contains aromatic compounds having 9 or more carbon atoms per molecule.
Generally, the process effluent can be separated into these principal fractions by any known method(s) such as, for example, fractionation distillation. Because the separation method(s) are well known to one skilled in the art, the description of such separation method(s) is omitted herein. The intermediate fraction can be fed to an aromatization reactor to be converted to aromatic hydrocarbons. The methane, ethane, and propane can be used as fuel gas or as a feed for other reactions such as, for example, in a thermal cracking process to produce ethylene and propylene. The olefins can be recovered and further separated into individual olefins by any method(s) known to one skilled in the art. The individual olefins can then be recovered and marketed. The BTX fraction can be further separated into individual C6 to C8 aromatic hydrocarbon fractions. Alternatively, the BTX fraction can further undergo one or more reactions either before or after separation to individual C6 to C8 hydrocarbons so as to increase the content of the most desired BTX aromatic hydrocarbon. Suitable examples of such subsequent C6 to C8 aromatic hydrocarbon conversions are disproportionation of toluene (to form benzene and xylenes), transalkylation of benzene and xylenes (to form toluene), and isomerization of meta-xylene and/or ortho-xylene to para-xylene.
After the improved zeolite catalyst composition has been deactivated by, for example, coke deposition or feed poisons, to an extent that the feed conversion and/or the selectivity to the desired ratios of olefins to BTX has become unsatisfactory, the improved zeolite catalyst composition can be reactivated by any means or method(s) known to one skilled in the art such as, for example, calcining in air to burn off deposited coke and other carbonaceous materials, such as oligomers or polymers, preferably at a temperature in the range of from about 400xc2x0 C. to about 1000xc2x0 C. The optimal time periods of the calcining depend generally on the types and amounts of deactivating deposits on the catalyst composition and on the calcination temperatures. These optimal time periods can easily be determined by those possessing ordinary skill(s) in the art and are omitted herein for the interest of brevity.
The following examples are presented to further illustrate this invention and are not to be construed as unduly limiting its scope.